Electronic Theses and Dissertation

Susu merupakan bahan pangan hewani yang kaya akan protein, lemak, vitamin, mineral, dan laktosa, namun mudah rusak karena mendukung pertumbuhan mikroorganisme. salah satu upaya untuk meningkatkan mutu, keamanan, dan masa simpan susu adalah melalui fermentasi menggunakan bakteri asam laktat (bal), seperti lactobacillus acidophilus dan bifidobacterium longum, yang juga menghasilkan produk probiotik dengan aktivitas antioksidan dan antibakteri. pengembangan susu fermentasi dapat dilakukan dengan penambahan puree bengkuang (pachyrhizus erosus), yang mengandung vitamin c, senyawa fenolik, flavonoid, dan inulin sebagai prebiotik. kandungan tersebut berpotensi meningkatkan pertumbuhan bakteri probiotik serta aktivitas antioksidan dan antibakteri. namun, penelitian mengenai pemanfaatan puree bengkuang pada susu fermentasi terhadap kualitas mikrobiologi, aktivitas antioksidan, dan aktivitas antibakteri masih terbatas. penelitian ini bertujuan untuk menganalisis pengaruh penambahan puree bengkuang terhadap kualitas susu fermentasi yang ditinjau dari total plate count (tpc), aktivitas antioksidan, dan aktivitas antibakteri terhadap escherichia coli dan staphylococcus aureus. penelitian dilaksanakan pada bulan april 2026 di laboratorium ilmu dan teknologi pengolahan susu serta laboratorium analisis pangan dan hasil pertanian, universitas syiah kuala. penelitian menggunakan rancangan acak lengkap (ral) yang terdiri atas empat perlakuan, yaitu p0 (0%), p1 (15%), p2 (20%), dan p3 (25%) yang masing-masing dilakukan sebanyak empat ulangan sehingga diperoleh 16 satuan percobaan. dimana sampel yang diujikan hanya 8 satuan percobaan pada ulangan ke-1 dan ulangan ke-3. susu kambing difermentasi menggunakan starter lactobacillus acidophilus dan bifidobacterium longum sebanyak 5% (v/v), kemudian diinkubasi pada suhu 37°c selama 18 jam. data hasil pengamatan dianalisis secara deskriptif dan disajikan dalam bentuk grafik. hasil penelitian menunjukkan bahwa penambahan puree bengkuang mampu mempertahankan bahkan berpengaruh terhadap jumlah bakteri asam laktat pada susu fermentasi dengan nilai total plate count (tpc) berkisar antara 8,90–9,15 log cfu/ml, sehingga seluruh perlakuan memenuhi standar sni susu fermentasi. nilai tpc tertinggi diperoleh pada perlakuan p3 (25%) sebesar 9,15 log cfu/ml. aktivitas antioksidan terbaik juga diperoleh pada perlakuan p3 (25%) dengan nilai ic₅₀ sebesar 7,48 µg/ml atau ppm, yang termasuk dalam kategori antioksidan sangat kuat. sementara itu, aktivitas antibakteri terbaik diperoleh pada perlakuan p1 (15%), dengan zona hambat terhadap escherichia coli sebesar 2,50 mm dan terhadap staphylococcus aureus sebesar 3,25 mm, meskipun keduanya masih tergolong dalam kategori daya hambat lemah. dengan demikian, penambahan puree bengkuang berpotensi meningkatkan karakteristik fungsional susu fermentasi sehingga layak dikembangkan sebagai minuman pangan fungsional dengan aktivitas antioksidan dan antibakteri.

Milk is an animal-derived food that is rich in protein, fat, vitamins, minerals, and lactose. However, it is highly perishable due to its ability to support the growth of microorganisms. One approach to improving the quality, safety, and shelf life of milk is fermentation using lactic acid bacteria (LAB), such as *Lactobacillus acidophilus* and *Bifidobacterium longum*. These microorganisms also produce probiotic fermented milk with antioxidant and antibacterial properties. The development of fermented milk can be enhanced by the addition of yam bean (*Pachyrhizus erosus*) puree, which contains vitamin C, phenolic compounds, flavonoids, and inulin as a prebiotic. These bioactive compounds have the potential to promote the growth of probiotic bacteria while enhancing antioxidant and antibacterial activities. Nevertheless, studies investigating the effects of yam bean puree on the microbiological quality, antioxidant activity, and antibacterial activity of fermented milk remain limited. This study aimed to evaluate the effect of yam bean puree addition on the quality of fermented milk in terms of Total Plate Count (TPC), antioxidant activity, and antibacterial activity against *Escherichia coli* and *Staphylococcus aureus*. The experiment was conducted in April 2026 at the Dairy Science and Processing Technology Laboratory and the Food and Agricultural Product Analysis Laboratory, Syiah Kuala University. A Completely Randomized Design (CRD) was employed, consisting of four treatments: P0 (0%), P1 (15%), P2 (20%), and P3 (25%) yam bean puree addition, with four replications for each treatment, resulting in 16 experimental units. However, only eight experimental units from the first and third replications were selected for analysis. Goat milk was fermented using a 5% (v/v) mixed starter culture of *Lactobacillus acidophilus* and *Bifidobacterium longum*, followed by incubation at 37°C for 18 hours. The observational data were analyzed descriptively and presented in graphical form. The results showed that the addition of yam bean puree maintained and influenced the population of lactic acid bacteria in fermented milk, with Total Plate Count (TPC) values ranging from 8.90 to 9.15 log CFU/mL. All treatments met the Indonesian National Standard (SNI) requirements for fermented milk. The highest TPC value was observed in treatment P3 (25%), reaching 9.15 log CFU/mL. The highest antioxidant activity was also obtained in treatment P3 (25%), with an IC₅₀ value of 7.48 µg/mL (ppm), which is classified as a very strong antioxidant. Meanwhile, the highest antibacterial activity was observed in treatment P1 (15%), with inhibition zones of 2.50 mm against *Escherichia coli* and 3.25 mm against *Staphylococcus aureus*, although both were still categorized as exhibiting weak antibacterial activity. Overall, the addition of yam bean puree has the potential to enhance the functional properties of fermented milk, making it a promising functional beverage with antioxidant and antibacterial activities.